A female restaurant manager at the scene, who would not give her name, asked that the employees be left alone, saying they "are going through a lot.''

Other employees standing outside said they'd been asked not to talk to the press.

The restaurant is part of the national Steak n Shake chain based in Indianapolis.

"Our hearts go out to the families of the associates who were killed in this senseless act of violence," Sardar Biglari, chairman and chief executive officer of the restaurant chain, said in a statement.

"We will do everything possible to help their families during this difficult time and will cooperate fully with the authorities to help bring those responsible to justice.''

The restaurant is located along a busy commercial thoroughfare of car dealers, big-box stores, small businesses and restaurants in a tiny, middle-class community of Green Park in St. Louis County, about 10 miles outside the city limits of St. Louis.

The restaurant ordinarily is open 24 hours, but had closed at midnight for routine pest extermination, and was to have reopened Monday morning. Panus said investigators believe the robbery and homicides occurred sometime between 2:30 and 4:30 a.m.

Police asked the public for any information that would help them solve the crimes.

Investigators were checking to see if any of the surrounding businesses may have captured any activity on surveillance tapes. Panus wouldn't say whether the restaurant had surveillance cameras.